Planning for Installation

DFSMSdfp Storage Administration Reference

Using Data Sets

SHAREOPTIONS (X 4)

Cross-system SHR(x 4) provides the same limited protection across systems as cross-region SHR(4). Extensions of the data sets high-used RBA are prohibited. To provide complete integrity protection it is the users responsibility to write Assembler routines using the RESERVE/RELEASE macros in addition to the ENQ/DEQ macros required for cross-region. This is a complex undertaking. If it was simple and/or if performance was acceptable, OS/390 VSAM would have implemented it. Alternatives to complete DASD sharing of VSAM data sets should be considered first. See DFSMS/MVS Using Data Sets, SC26-4922, for greater detail on coding RESERVE/RELEASE routines and the alternatives.

SHAREOPTIONS (X 3)

If SHR(x 3) is used, all data set opens are allowed across systems. OS/390 VSAM provides no protection for the data set.

5.6.6.4 DASD Sharing Considerations

A second system opening a data set that is open for output on another system will receive the OPEN return code 116 (X′74′) which indicates the data set was

not properly closed. VSAM will automatically issue the VERIFY macro for the program.

Once the data set is open, a cross-system program must contend with the possibility that the data, indexes, extents, the RBA of records, and the High-Used-RBA of the data set may be changing due to updates in another system. This may cause VSAM error codes and/or abends of the programs using the data set.

Alternatives to VSAM Data Set Sharing

Probably the simplest way to avoid the problems of cross-system and

cross-region sharing is to schedule all data set access through a single system and address space. This generally means that batch updates must be performed while the files are unavailable to CICS systems.

CICS VSAM data sets can be accessed from multiple CICS address spaces via the CICS Multiple Region Option (MRO) or across systems with Inter-Systems Communication (ISC). However, there is no CICS support for cross-region or cross-system sharing of VSAM data sets with batch jobs.

IMS/VS DC and DB offer methods of cross-system and cross-region sharing of DL/I (IMS) data bases via the IMS Resource Lock Manager (IRLM) and Data Base Resource Control (DBRC). See the appropriate IMS/VS manuals for details.

CICS/OS provides for cross address space sharing of IMS/VS data bases via the CICS Shared Data Base facility.

The DB2 Transparency Feature allows some VSAM files to be loaded into DB2 table spaces and accessed with existing batch or CICS/OS VSAM applications.

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IBM OS/390 manual Dasd Sharing Considerations, Alternatives to Vsam Data Set Sharing

OS/390 specifications

IBM OS/390, a versatile operating system, was a cornerstone in enterprise environments and played a pivotal role in mainframe computing. Released in the mid-1990s, OS/390 combined the strengths of IBM's MVS (Multiple Virtual Storage) with new features and enhancements, targeting scalability, reliability, and performance in demanding business applications.

One of the key features of OS/390 was its robust support for multiple users and processes. The system allowed thousands of concurrent users to access applications and data, ensuring high availability and minimizing downtime—a critical requirement for many large organizations. This scalability was supported through various enhancements in memory management and processor scheduling, enabling optimal resource allocation across diverse workloads.

OS/390 was known for its superior workload management capabilities. The Workload Manager (WLM) component allowed administrators to define service policies, specifying how system resources would be allocated according to the priority of tasks. This ensured that critical business processes received the necessary resources while less critical tasks were managed more flexibly.

Another significant characteristic of OS/390 was its commitment to security. The operating system provided comprehensive security features, including user authentication, data encryption, and auditing capabilities. This focus on security was vital for organizations handling sensitive data, ensuring compliance with regulations and safeguarding against unauthorized access.

OS/390 also supported advanced technologies that facilitated integration and development. The system included features like the IBM CICS (Customer Information Control System) for transaction processing and IMS (Information Management System) for database management. These technologies allowed organizations to build robust, high-performance applications tailored to specific business needs.

The ease of network integration was another strength of OS/390. With the advent of the Internet and global connectivity, OS/390 systems could easily interface with various network protocols, enabling businesses to operate in a connected world. This inclusion paved the way for many organizations to expand their capabilities and offer new services, driving digital transformation.

In conclusion, IBM OS/390 represented a significant advancement in mainframe technology, combining scalability, security, and robust workload management. Its rich feature set and support for critical enterprise applications solidified its role as a vital component of many organizations' IT infrastructures, ensuring they could meet their operational challenges head-on while supporting future growth. As technology continues to evolve, the legacy of OS/390 remains influential in the realm of computing.